industrial CO2 recovery techniques and the aquarium

[Vaevictus]

Since my tap water is really hard and contains lots of carbonate (CO3 2-) I thought it would be really cool if there was something I could do to the water while it was in the tank to convert the carbonate to CO2.

Well, it seems like lots of research is going on with carbon capture, to capture gases from chimneys etc and capture the CO2 in solution, then later recover the CO2 from the solution.

I came across this PDF http://www.netl.doe.gov/publications/pr ... ue_194.pdf

It's a while since I studied chemistry but if I am understanding it correctly I will try and summarise the PDF:

The paper describes a simple device through which you feed a solution containing carbonate ions (eg our fish tank water).
An electrical current is passed through it. The electric current causes changes in PH of the solution which causes the dissolved carbonate to turn into co2 gas.

The energy used in this process is very low: 0.57kWh of electricity needed to generate 1KG of CO2......

What I would like to know is, could this technology be applied on a small scale for the aquarium to produce CO2 from the natural hardness in the water? People with soft water could buy sodium hydrogen carbonate powder (which I would imagine is dirt cheap) and make up strong solutions to feed this device and get CO2.

I have sunk a good bottle of wine so this may be a ridiculous idea I hope it could make some interesting discussion though

Vae

 

[ceg4048]

Hi,
Yes, it's already been developed. It was a construct of The Matrix and it's been a disaster at the hobby level for years. See the thread http://ukaps.org/forum/viewtopic.php?f=37&t=3895&p=43209

I'd stick with pressurized gas for now, until Lt. Commander Data and Jordi figure something else out in Star Trek - New Generation. I'm still holding out for some kind of a Matter/Anti-Matter device.

A 0.6 Kilowatt-hour is not exactly minor. That's 600 watt-hours. So that's the energy consumed by a 60 watt bulb burning for 10 hours. I guess you'd have to compare your kilowatt-hour charges to what you pay for a fire extinguisher re-fill though. In any case, those existing technology Carbo+ units will take about 2 years to produce 1Kg of gas - if they last that long.

Cheers,

 

[Vaevictus]

Hi,

This is a totally different method to the product you linked to, and has been proven efficient enough to be used in industry.

0.6 kWh to produce 1KG CO2 will cost you about 10pence. The system would need the alkali solutions to be pumped around though so add another 20 watts when in use.

Read the pdf ceg, this is a completely different thing!

 

[ceg4048]

Hi,
Well I can't see how this differs all that much from hydrolysis using electrolytic plates. The unit has to be mounted in the tank, which means you can't expose it to the electrolyte. That's why they use carbon plates in the aquarium units. Our units convert the bicarbonates in the tank water to CO2.

Remember you also have to pressurize the gas if it's done externally to make it useful and I that'sll cost money.

Apologies for being so dim. Could you help me figure out the fundamental difference?

Cheers,

 

[Vaevictus]

The difference between this and the shitty carbon plate electrolysis method is that this method would take either the tank water in or some DIY high conc. carbonate solution (which would be cheap) and create CO2 from it.

The bubbles created would not need to be pressurised, they could be fed by conventional means into a reactor or straight into your canister filter.

This unit would be OUTSIDE the aquarium.

dont apologise - I only find this method interesting on paper it may not be feasible for an aquarium. The size of the device, the performance with low-conc. carbonate solutions etc may not be appropriate.

Hopefully a cleverer guy than us will get a whiff of this thread and provide insight

 

[ceg4048]

You cannot feed any gas into a tank unless it's at a higher pressure than the static pressure of your water at the point of injection. Additionally, the CO2 concentration will absolutely depend on the pressure of the gas. Whether it's DIY CO2 from an organic source, this device, or from a pressure vessel, you must have a higher pressure. That's one of the reasons the Carbo+ unit is so miserable.

If the unit is external, then you have to separate the gas, which one of the schematics shows, then you have to pressurize it to greater than 1 bar (ideally 1.5 to 2 bars) then send it back into the tank. It may be though that the gas produced is already at a higher pressure so this might not be a big deal. And of course it would be a good idea if it were regulated, so you still need similar hardware as that of the pressurized cylinder, otherwise you have the same stability issues as a yeast based system. Seems like this would be one of the limiting factors. Perhaps the yield and pressure can be controlled by controlling the current at the electrodes. The yield will also depend on the KH of the water so there might be some threshold KH value that would make it worthwhile.


Cheers,